Middle cerebral artery blood velocity during exercise in patients with atrial fibrillation

Atrial fibrillation limits the ability to increase cardiac output during exercise and may, in turn, affect the exercise-associated elevation in cerebral perfusion. In nine patients with atrial fibrillation (AF) and in five age-matched healthy subjects, middle cerebral artery blood velocity (MCA V-mean) was measured during incremental exercise using the transcranial Doppler. The AF patient group exhibited a lower aerobic capacity than the control group [peak work rate: 106 W (71-153 W; median and range) vs. 129 W (118-159 W) and maximal oxygen uptake: 1.41 min(-1) (1.0-1.91 min(-1)) vs. 1.71 min(-1) (1.4-2.21 min(-1)); P = 0.05]. At rest, MCA V-mean was not significantly different between the two groups [43 cm s(-1) (39-56 cm s(-1)) vs. 52 cm s(-1) (40-68 cm s(-1))]. During intense cycling, the increase in MCA V-mean was to 51 cm s(-1) (40-78 cm s(-1)) (9%) in the AF group and lower than in the healthy subjects [to 62 cm s(-1) (50-81 cm s(-1)) 23%; P<0.05], which corresponded with the smaller than expected increase in cardiac output [156% (130-169%) vs. 180%]. Thus, there was a correlation between the increase in MCA V-mean and the ability to increase cardiac output (r(2) = 0.55, P<0.01). We suggest that, during exercise with a large muscle mass, atrial fibrillation affects the ability to elevate cerebral perfusion, and this results from an impaired ability to increase cardiac output.